i) Field of the Invention
The present invention relates to measurement devices that comprise an authentication module for verifying the authenticity of an associated unit and in particular to measurement systems that comprise a measurement probe mountable to co-ordinate positioning apparatus.
ii) Description of Related Art
Measurement probes for use with co-ordinate positioning apparatus, such as co-ordinate measuring machines, machine tools, inspection robots etc, are known. Examples of such measurement probes are described in US4153998, WO2004/57552 and WO2007/28964.
To offer flexibility to users, measurement devices for use with co-ordinate positioning apparatus are often produced and sold as discrete modular units that are combined to establish a system that can perform the required measurement task. For example, a range of different measurement probes are often produced for use with a number of measurement probe interfaces. An appropriate measurement probe and probe interface can then be used in combination by an end user. For machine tool based probing applications, data transfer between the measurement probes and probe interface may take place over a wireless (e.g. RF or optical) link using a communications protocol such as that described in WO2004/57552 or WO2007/28964.
Although providing such modular apparatus offers the advantage of increased flexibility, it has the disadvantage that ill-informed users may attempt to combine measurement probe products that are in some way incompatible. Furthermore, the communication protocols of existing wireless communication systems can typically be easily copied thereby allowing third parties to produce devices that attempt to mimic genuine devices. The quality of such third party devices can be highly variable and the compatibility of such devices with genuine articles is typically not properly tested. The combination of incompatible apparatus, or the use of apparatus from unauthorised third party manufacturers, can thus result in measurement systems being established that do not provide an acceptable level of measurement accuracy.